The present invention relates to archery bows and particularly to an improved bow limb of laminated resin-supported fiber construction useable either in a compound bow or a conventional bow.
In the past, archery bow limbs have included laminations of parallel glass fibers in a matrix of plastic resin material. Such laminations have been attached by adhesives to the back (the tension side) and belly (the compression side) of a core of wood or laminated wood construction to form such limbs. In construction of bow limbs having reflex curvature, recurvature, or deflex curvature, and particularly in such curved limbs for use in compound bows, the inclusion of such wooden cores has conventionally been thought necessary to avoid failure of the limbs.
Previously, it has been found necessary to include a core of wood between layers of materials such as fiber-reinforced resins adhesively attached to the back face and to the belly side of a bow whose limbs have any curvature when relaxed, because the absence of such a core has resulted in failure of the bow, should the string be released from a drawn position. The shock imposed on the materials of the belly laminations of conventional bows, including bows which include a wooden core between back and belly laminations, usually results in rapid failure of the belly laminations when the bowstring is released without the load of an arrow being shot.
The compound bow, a bow of the type first described in Allen U.S. Pat. No. 3,486,495, includes eccentric wheels or cams mounted on the tips of the bow limbs and interconnected with the bowstring by cables which make it possible to draw and hold bows whose limbs are stiffer than those of a traditional bow the same person would be able to draw. Compound bows are thus able to store increased amounts of potential energy for a given amount of tension present in the bowstring when the bow is in its fully drawn position. The limbs of compound bows are even more likely than traditional bows to fail if the bowstring is released from a drawn position without an arrow to provide a load during return of the bowstring to its straight stretched position.
For the sake of greater accuracy, it is desired to provide bows capable of propelling arrows of a given weight at a higher initial velocity than has previously been possible. This requires limbs of the bow to provide a greater amount of bowstring tension throughout a larger part of the length of the draw, yet the limb must be light enough to accelerate quickly when the bowstring is released to shoot an arrow. In the past, however, it has not been known how to build such a bow limb which is not subject to failure if the bowstring is released without an arrow.
One attempt to avoid the use of a wooden core in a bow limb is described in Pierson et al., U.S. Pat. No. 2,894,503, in which a core of randomly oriented glass fibers contained in a resin matrix extends the entire length of a bow limb between the belly and back layers.
Bear, U.S. Pat. No. 2,665,678, discloses a bow including glass fiber reinforcement in laminae supported by a wooden core, with the laminae being assembled in a pre-stressed condition.
DeGiacomo, U.S. Pat. No. 2,815,015, describes a bow of similar construction in which epoxy resins are used to protect and interconnect the glass fibers reinforcing the laminae.
Eicholz, U.S. Pat. No. 3,850,156, discloses a bow whose limbs have a laminated wood core and multiple laminations of glass fiber-reinforced material, with at least one lamina including diagonally oriented graphite fibers extending at an angle of about 30 degrees relative to the longitudinal axis of the bow limb.
Nevertheless, the need still remains for an improved bow able to withstand, unharmed, repeated release of the bowstring from a fully drawn condition without shooting an arrow, and a method for producing such a bow having limbs capable of imparting a greater amount of energy to an arrow, in order to cast the arrow at a greater initial velocity than previously has been possible using bow limbs including pre-stressed laminae attached to wooden or other cores.